In the past, solid polymer fibers have traditionally been made on a stationary spinneret from which fibers are pulled or drawn. This is known as a "textile process". It is also known to make hollow polymer fibers using a textile process. They are lighter in weight than solid polymer fibers having the same length and diameter. Because they can often provide the same performance at reduced weight, hollow polymer fibers are sometimes more useful in certain applications than solid polymer fibers. For example, the reduced weight is particularly desirable when the hollow polymer fibers are used as apparel insulation fibers and in certain other insulation applications. Unfortunately, the textile process for making hollow polymer fibers has a limited throughput, because the process relies solely on mechanical attenuation to form the molten polymer into fibers.
Polymer microfibers are very small diameter fibers that are particularly suited for certain applications such as thermal and acoustical insulation, absorbent products and filtration products. The textile process is not well adapted for making polymer microfibers because there is a limit on how small the diameter of the fibers can be formed with mechanical attenuation. It is known to make solid polymer microfibers by a melt blowing process which utilizes a stream of air to attenuate the fibers. However, it is not known to make hollow polymer microfibers by the melt blowing process. The stream of air attenuating the fibers would likely interfere with the introduction of gas inside the fibers to make hollow fibers. Further, the melt blowing process is very expensive. Thus current polymer technology does not provide a way to make directly spun hollow polymer microfibers.
Therefore, it would be desirable to provide a process for making hollow polymer fibers that has a higher throughput than the textile process. It would particularly be desirable to provide a process for making hollow polymer microfibers.